SWODY1
SPC AC 141240
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0740 AM CDT WED SEP 14 2011
VALID 141300Z - 151200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A DEVELOPING CLOSED LOW WILL MOVE OVER SRN JAMES BAY AS AN UPSTREAM
SHORTWAVE TROUGH DIGS SEWD FROM ND TO LAKE MI BY LATE TONIGHT. AT
THE SURFACE...A LARGE/COOL SURFACE RIDGE IS SPREADING SWD/SEWD
ACROSS THE PLAINS/MS VALLEY IN THE WAKE OF THE AMPLIFYING MIDLEVEL
TROUGH. THE COLD FRONT DEMARCATING THE COOL SURFACE RIDGE WILL BE A
PRIMARY FOCUS FOR THUNDERSTORM DEVELOPMENT NEAR AND E OF THE MS
RIVER TODAY INTO TONIGHT. FARTHER W...THE WEAK CLOSED LOW INVOF NW
AZ WILL DRIFT EWD THROUGH TONIGHT...WHILE A POST-FRONTAL UPSLOPE
FLOW REGIME WILL BECOME ESTABLISHED ACROSS W TX/ERN NM.
...CENTRAL APPALACHIANS TO SE NEW ENGLAND THIS AFTERNOON...
AN INITIAL COLD FRONT FROM YESTERDAY WILL DRIFT SLOWLY SEWD ACROSS
WV/PA/SE NEW ENGLAND TODAY...PROVIDING A FOCUS FOR AT LEAST ISOLATED
THUNDERSTORM DEVELOPMENT. BOUNDARY LAYER DEWPOINTS IN THE LOW-MID
60S AND SURFACE HEATING WILL BOOST AFTERNOON MLCAPE TO 500-1500 J/KG
ALONG THE FRONT...WHICH WILL ALSO CORRESPOND TO THE SERN FRINGE OF
THE STRONGER BELT OF SWLY MIDLEVEL FLOW. THE NET RESULT WILL BE THE
POTENTIAL FOR A NARROW ZONE OF ORGANIZED MULTICELL/MARGINAL
SUPERCELL POTENTIAL WITH AN ATTENDANT RISK FOR ISOLATED
STRONG/DAMAGING WINDS AND MARGINALLY SEVERE HAIL FOR A FEW HOURS
THIS AFTERNOON.
...ERN AR/WRN TN/NW MS TODAY...
A SURFACE LOW ALONG THE COLD FRONT IN NW AR IS EXPECTED TO MOVE EWD
TOWARD THE MS RIVER AND WEAKEN THIS AFTERNOON...IN ADVANCE OF A
WELL-DEFINED MCV NOW TRAVERSING N CENTRAL OK. A NARROW CORRIDOR OF
BOUNDARY LAYER DEWPOINTS NEAR 70 F EXTENDS NWD ACROSS LA TO CENTRAL
AR TO THE SE OF THE LOW...AND THIS MOISTURE WILL COINCIDE WITH THE
ERN EXTENT OF A STEEP LAPSE RATE PLUME FROM THE SRN PLAINS.
HOWEVER...WIDESPREAD CLOUDS WILL TEND TO LIMIT SURFACE HEATING AND
THE POTENTIAL FOR STRONGER DESTABILIZATION THIS AFTERNOON. MLCAPE
WILL STILL REACH 1500-2500 J/KG IN AN ENVIRONMENT WITH 30-40 KT
EFFECTIVE BULK SHEAR...THUS A FEW ORGANIZED MULTICELL CLUSTERS OR
SUPERCELLS CAN BE EXPECTED WITH THE POTENTIAL FOR ISOLATED DAMAGING
WINDS/LARGE HAIL. IF CLOUD BREAKS BECOME MORE EXTENSIVE THAN
CURRENTLY EXPECTED...A SMALL SLIGHT RISK MAY STILL NEED TO BE
CONSIDERED IN LATER UPDATES.
...ERN NM/W TX THIS AFTERNOON INTO TONIGHT...
SWLY MIDLEVEL FLOW WILL INCREASE GRADUALLY OVER NM AS THE AZ LOW
DRIFTS EWD...AND LOW-LEVEL UPSLOPE FLOW WILL INCREASE ACROSS THE SRN
HIGH PLAINS. LOW-LEVEL MOISTURE/INSTABILITY WILL LIKELY REMAIN
SOMEWHAT LIMITED ACROSS W TX/ERN NM...AND THIS WILL TEND TO LIMIT
STORM INTENSITY. HOWEVER...DEEP-LAYER VERTICAL SHEAR WILL BE
SUFFICIENT FOR SUPERCELLS...AND THERE WILL BE AT LEAST A LOW-END
RISK FOR HAIL/DAMAGING WIND THIS AFTERNOON INTO TONIGHT AS
CONVECTION INCREASES IN COVERAGE FROM ERN NM INTO W TX/THE TX
PANHANDLE.
..THOMPSON/HURLBUT.. 09/14/2011
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